The invention relates to the manufacture of a tire, the beads of which are without bead wires as means for absorbing the tensile stresses of the carcass reinforcement and as means for holding said beads securely on the rim seats on which said beads will be mounted.
Application FR 2 717 425 describes a tire with a radial carcass reinforcement extending from one bead to the other, surmounted radially by a crown reinforcement which in turn is surmounted by a tread, characterized in that each bead, which is without a bead wire, comprises firstly an annular element, the tensile strength of which in the circumferential direction is substantially less than that which would be necessary for a bead wire in a known tire of the same dimension, the axis of this annular element being the axis of revolution of the tire, and secondly a bead reinforcement armature made of at least two reinforcement layers in contact with or in proximity to the annular element, said reinforcement layers each comprising reinforcement elements which are parallel to each other in each layer, crossed from one layer to the adjacent layer, forming with the circumferential direction an angle xcex2 such that 0 less than xcex2xe2x89xa610xc2x0, all these layers having a resistance to rupture in traction at least equal to that which would be necessary for a bead wire in a known tire of the same dimension. The mechanical strength of the bead reinforcement armature is therefore the essential contribution to the mechanical resistance of the bead reinforcing assembly formed by the annular element and said armature, this assembly thus making it possible to replace the bead wire of a conventional tire. The carcass reinforcement winds around the annular element, and the reinforcement layers have their radially upper ends located in the bead at different heights.
The complex formed by the two layers of the bead reinforcement armature and possibly by the annular element, which is intended to facilitate manufacture of such a complex and consequently the tire, may be produced during said building of the blank on the building drum of the same name.
Whatever the method or process employed, the necessity of having angles of reinforcement elements of between 0xc2x0 and 10xc2x0, and preferably 520  or less, in the vulcanized tire results in serious difficulties when cutting the non-vulcanized plies of reinforcement elements to the desired angles, and also when butt-jointing the widths obtained, which difficulties may result in a loss of accuracy in the arrangement of the reinforcement layers relative to each other, but also relative to the products adjoining said layers. Said difficulties are also the cause of not inconsiderable losses of time in the industrial process, and increased manufacturing costs.
In order to overcome this state of affairs, the invention proposes, for the manufacture of a tire with radial carcass reinforcement extending from one bead to the other and with edges folded over to form carcass reinforcement upturns, each bead being without a bead wire and reinforced by a complex of axially adjacent layers of reinforcement elements which form with the circumferential direction an angle xcex2 such that 0xc2x0 less than xcex2xe2x89xa610xc2x0, the carcass reinforcement winding around said complex to form a carcass reinforcement upturn, a process characterised in that the complex of axially adjacent layers is manufactured separately from the carcass reinforcement blank, said manufacturing operation comprising the following steps:
a) laying at least one ply of reinforcement elements oriented at an angle xcex1, such that xcex1xe2x89xa710xc2x0, on a laying drum of radius R,
b) extending said ply by increasing the drum radius to a value R1 greater than R,
c) forming a cylindrical sleeve of two layers of elements crossed from one layer to the next, with an angle xcex1xe2x89xa710xc2x0,
d) increasing for a second time the radius of the laying drum to a radius R2 such that the final angle xcex2 of the reinforcements is obtained by pantograph effect,
e) finishing the building of the complex of adjacent layers,
f) removing the finished complex from its laying drum and laying it at the desired location on the building drum for the cylindrical carcass reinforcement blank.
The sleeve of two layers of crossed elements can advantageously be formed in two ways:
either the first step of manufacture consists in laying a single ply of parallel elements oriented at the angle xcex1, and the two crossed layers can be formed by folding over part of the ply on to the other part of said ply,
or the first step consists in laying two plies independently of one another on two independent laying drums of radii R and Rxe2x80x2, to make allowance for the thickness of one ply, and extending them to radii R1 and Rxe2x80x21, the two layers possibly being formed by superposition on the drum of radius R1.
In the former case above, once the folding-over of the ply on itself has been effected, the increase in the radius of the drum to the value R2 making it possible to arrive at the final angle xcex2, a complex formed of two folded-over layers of crossed elements is obtained directly.
In the second case in question, once the laying and superposition of two plies on the drum of radius R1 has been effected, the increase in the radius to the value R2 making it possible to arrive at the final angle xcex2, a complex formed of two non-folded-over layers of crossed elements is obtained directly, but the building of a complex of four folded-over layers can also be terminated by means of folding over the two plies of crossed elements on themselves at an angle xcex2.
The folding of one or more plies over on themselves may be effected with or without the aid of a circular ring, whether this folding be effected in the case of the radius R1 or whether it be effected in the case of the radius R2. In the former case in question, said circular ring is then provided with a low modulus of extension for a certain range of relative elongation xcex50 and a high modulus for the values of relative elongation outside the upper limit of said range, the relative elongation xcex50 corresponding to the passage from the radius R1 to the radius R2 and being equal to (R2xe2x88x92R1)/R1. In the latter case in question, the circular ring is inextensible.
The invention will be better understood with reference to the drawings appended to the description, illustrating in non-limitative manner examples of embodiments.